1. Field of the Invention
The invention relates to an improved fuel injector for an internal combustion engine.
2. Description of the Prior Art
At present, for introducing fuel into direct-injection, self-igniting internal combustion engines, stroke-controlled high-pressure reservoir systems (common rails) are also used. An advantage of the stroke-controlled systems is that the injection pressure can be adapted to the load and rpm. The stroke-controlled high-pressure reservoir injectors used at present include a piezoelectric actuator and a 3/2-way control valve for controlling the pressure in the needle control chamber. The injection valve member is controlled via a servo control chamber.
By means of an injection valve member controlled directly by the piezoelectric actuator, the opening and closing speed of the injection valve member can be increased compared to presently known injectors. A simpler injector construction is also possible. To achieve the necessary nozzle needle stroke, however, a very long piezoelectric actuator is necessary. A fuel injector with an injection valve member controlled directly by a piezoelectric actuator is known for instance from European Patent Disclosure EP A 0 995 901. This fuel injector includes an injection valve member, which opens or closes an injection opening into a combustion chamber of the engine. On the side of the injection valve member remote from the injection opening, there is a piezoelectric actuator in the injector housing. The piezoelectric actuator acts on a threaded rod, which in turns acts on the injection valve member via a spring element. The piezoelectric actuator is made with a very long length, in order to attain the necessary nozzle needle stroke.
To shorten the length of the piezoelectric actuator, a fuel injector is known from German Patent Disclosure DE A 102 20 498 in which a piezoelectric actuator controls a needle valve motion via a final control element motion-amplifying lever. The piezoelectric actuator acts on one side of the final control element motion-amplifying lever, which as a result experiences a rotary motion and thus with its other side triggers an injection valve member, which opens or closes injection openings.